An exemplary application for the present invention is in printers having a duplexing function. High-end printers on the market today are typically available, either as a standard feature or more often an optional feature, with a duplexer system to enable two-sided printing. A primary purpose of a duplexer is to turn-over the print media after printing on a first or “front” side, so that an image can be placed on the second or “back” side of the print media. Typically, for the example of a laser printer, the print media starts out in the printer input tray, is picked from the input tray, and transported to a printer registration assembly. After being deskewed by the registration assembly, the media is then transported through the imaging and fusing areas to a diverter assembly. The diverter assembly typically has two moveable paper guides that determine by their position the flow of the media. The print engine firmware controls electric solenoids to determine the position of these guides. The first guide or diverter determines whether the sheet is diverted into the duplexer, or is allowed to continue on to one of the output destinations. The second diverter determines whether the sheet will be diverted to the face-down output bin or will continue straight out of the engine to the face-up output bin.
A significant challenge to the printing industry is aligning the backside image (second side printed) with the front side image (first side printed). This is especially true when the image is “full bleed” (i.e. the image extends to the edge of the sheet or page), which can be achieved through the more common process of post printing trimming operations or printing right to the edge of the page with zero margins.
Standard duplexing operations use one edge for page registration when printing the first image and the opposite edge of the media for registering the second printed image. In other words, the leading edge of the media when the first image is printed becomes the trailing edge for printing the second image. The leading and trailing edges of a print media vary in both length and parallelism. This presents problems in aligning the first side and second side images.
There are also inaccuracies in the absolute and relative placement of the lateral edge of the media on both the front side and the back side. Mechanical guides have been employed in the past to help steer the media.